Here are the diagnostic/testing manuals for the 2006 Sprinter. The US Airstream Westfalias are built on a 2004 chassis, but the differences should be minimal, or none.

There are four parts to the manual:

• 2006 Sprinter Service Manual: Body
• 2006 Sprinter Service Manual: Chassis
• 2006 Sprinter Service Manual: Powertrain
• 2006 Sprinter Service Manual: Transmission

Thanks to Juju for these manuals!